There is known an overflow valve (U.S. Pat. No. 3,005,507), comprising a hollow body with side ports which accommodates a spring-loaded sleeve with provision for moving along the body, while the side ports area carries another sleeve with a seat to interact with the spring-loaded sleeve. In the original position the spring-loaded sleeve is in the uppermost position, the side ports of the body below the spring-loaded sleeve are open allowing fluid to freely pass from the inner space of a drill string into the well and in the opposite direction. When running a drill string with an overflow valve into the well filled in with fluid, as well as when pulling it out, the spring-loaded sleeve is held in the uppermost position due to the spring elastic force. As this takes place, the side ports of the body are open to allow fluid outgoing from the well to fill in the inner space of the drill string as it is run into the well. As the drill string is pulled out, fluid flows from the inner space of the drill string into the well.
When drilling fluid is pumped under pressure into the drill string, the spring-loaded sleeve is brought to the lowermost position with the drilling fluid flow and is tightly pressed against the seat of the fixed sleeve. Thus, the spring-loaded sleeve closes the side ports of the body. The overflow valve is shut off. With the delivery of drilling fluid into the drill string cut off, the spring-loaded sleeve is brought to the uppermost position due to the spring elastic force, the side ports of the body being open to enable fluid to freely pass from the inner space of the drill string into the well and in the opposite direction. The overflow valve is open. During operation of the valve, the sleeves are subject to excessive wear, the springs fail, become no more elastic and break. The sleeves also collide when in operation, which results in their breakdown and, hence, in failure of the overflow valve. The overflow valve in question features a large number of components in need of high surface finish and accuracy. All this fails to ensure reliable and trouble-free operation of the overflow valve.
There is known an overflow valve (FR, A, 2,486,996), comprising a hollow body with side ports which accommodates a sleeve with holes. Fitted inside the sleeve is a seat to interact with a shut-off element located inside the hollow body, The shut-off element is in fact a spring-loaded rod whose lower and carries a disc and a cup seal.
In the original position the spring-loaded rods holds the disc and cup seal in the uppermost position. In doing so, a gap is provided between the disc, cup seal and seat through which fluid inside the overflow valve can freely pass into the well. Such is the condition of the overflow valve when the drill string is run into the well filled in with fluid and when it is pulled out.
When drilling fluid is pumped under pressure through the drill string into the overflow valve, the rod goes down under the action of the drilling fluid flow to close the gap between the seat and disc. The overflow valve is shut off. Drilling fluid flows through the sleeve holes to downhole mechanisms. With the delivery of drilling fluid into the overflow valve cut off, the rod backs the disc away from the seat due to the spring elastic force, and the overflow valve becomes open. The known overflow valve is characterized by excessive wear and premature failure of its components. The valve also features coil springs subject to ageing and breakdown which result in failure of the overflow valve. Besides, the drilling fluid flow in the known overflow valve passes mostly through the sleeve holes whose flow section is some minor part of that of the drill string opening. Hence, the hydraulic resistance of the overflow valve is large. Excessive wear and premature failure of the components are common. All this affects operating reliability and durability of the overflow valve.
There is known a drill string overflow valve (SU, A, 898,028), comprising a hollow body with side ports, a seat and a shut-off element fitted inside the hollow body.
In the known drill string overflow valve, the shut-off element is in fact a spring-loaded plunger fitted to which is a sleeve with holes and a turret. The body is provided with a stepped cage with a turret inside. In its lower part, the spring-loaded plunger is plugged, provided with holes and a ring lug. In the original position, the spring-loaded plunger is in the uppermost position. The holes of the seat and sleeve of the spring-loaded plunger are open. The inner upper part of the drill string overflow valve communicates with the well. As the drill string with the overflow valve is run into the well, the plunger is held in the uppermost position, fluid entering the inner upper part of the overflow valve and filling in the drill string through the side ports provided in the body, holes provided in the seat, sleeve and plunger, as well as through the gap between the turret and stepped cage. As the drill string is pulled out, fluid passes from the drill string into the well. When drilling fluid is pumped under pressure into the drill string, the plunger is brought to the lowermost position by the drilling fluid flow, the plunger holes open and the drilling fluid passes through into the lower inner part of the overflow valve and further to downhole mechanisms. With the delivery of drilling fluid into the drill string cut off, the plunger moves to the uppermost position due to the spring elastic force, the plunger holes close and holes provided in the plunger sleeve and seat open. The overflow valve is open.
The known overflow valve of the drill string comprises a large number of movable parts and units, a spring which loses its elasticity under the well conditions, becomes brittle and break, and seals with are subject to wear.
The small holes for fluid to pass are a source of high hydraulic resistance and, hence, of additional losses. The plunger plugged in its lower part impedes the main flow of drilling fluid delivered to downhole mechanisms. All this affects operating reliability and durability of the overflow valve.